OBJECTIVE The use of transthoracic Doppler echocardiography (TTDE) to evaluate the patterns and technique of measuring of left atrial appendage (LAA) flow velocities in normal cats. BACKGROUND Left atrial enlargement and dysfunction are characteristic features of feline cardiomyopathy that may cause blood stasis in the left atrium (LA). This low flow state may be associated with hypercoagulability and thrombus formation. Left atrial enlargement, spontaneous echocardiographic contrast, and decreased velocity of LAA flow may be early indicators of thromboembolic risk. Little is known about the patterns and determination of LAA flow in normal cats. METHODS Transthoracic Doppler echocardiography was used to evaluate LAA flow in 47 normal cats and to assess the effects of age, body weight, sex, heart rate, arterial blood pressure, and echocardiographic indices of LA and LV size and function on LAA flow variables. RESULTS Adequate LAA flow signals could be recorded in 43 (92%) cats. Polyphasic LAA flow profiles were obtained in all cats, consisting of two (79%), three (16%), or four (5%) flow waves. Maximum LAA flow velocity (mean+/-SD) was 0.47+/-0.20m/s (range 0.24-1.00) and average LAA flow velocity was 0.42+/-0.17m/s (0.22-0.93). There was a weak correlation between LAA flow velocity and LA size based on maximum LA diameter (r=0.36, p=0.018) and maximum LA area (r=0.44, p=0.004). There was no association between LAA flow velocity and any other independent variable evaluated. CONCLUSIONS LAA flow may be recorded by use of TTDE in cats. The results of this study can be used for comparison with LAA flow patterns found in disease states.